We apply a deep convolutional neural network segmentation model to enable novel automated microstructure segmentation applications for complex microstructures typically evaluated manually and subjectively. We explore two microstructure segmentation tasks in an openly available ultrahigh carbon steel microstructure dataset: segmenting cementite particles in the spheroidized matrix, and segmenting larger fields of view featuring grain boundary carbide, spheroidized particle matrix, particle-free grain boundary denuded zone, and Widmanstätten cementite. We also demonstrate how to combine these data-driven microstructure segmentation models to obtain empirical cementite particle size and denuded zone width distributions from more complex micrographs containing multiple microconstituents. The full annotated dataset is available on materialsdata.nist.gov.

In situ transmission electron microscope (TEM) characterization techniques provide valuable information on structure–property correlations to understand the behavior of materials at the nanoscale. However, understanding nanoscale structures and their interaction with the electron beam is pivotal for the reliable interpretation of in situ/ex situ TEM studies. Here, we report that oxides commonly used in nanoelectronic applications, such as transistor gate oxides or memristive devices, are prone to electron beam induced damage that causes small structural changes even under very low dose conditions, eventually changing their electrical properties as examined via in situ measurements. In this work, silicon, titanium, and niobium oxide thin films are used for in situ TEM electrical characterization studies. The electron beam induced reduction of the oxides turns these insulators into conductors. The conductivity change is reversible by exposure to air, supporting the idea of electron beam reduction of oxides as primary damage mechanism. Through these measurements we propose a limit for the critical dose to be considered for in situ scanning electron microscopy and TEM characterization studies.

Silicon dioxide (SiO2) has been the most important insulator in the highly-developed field of silicon (Si) technology. Accurate pitch and gate linewidth measurements for SiO2/Si systems (systems with a SiO2 insulating layer and Si substrate) have become necessary. Studying one such system obviously presents different results from that of the widely researched Si/Si structure, because the edge profile of the secondary electron (SE) signal contains contributions from two materials. In this work, several scanning electron microscope (SEM) images and SE profiles of SiO2/Si pitch and trapezoidal line structures, using various geometric and experimental parameters, were simulated through the use of Monte Carlo (MC) methods. It was found that, in contrast to Si/Si systems, the height of the insulating layer cannot be ignored during the evaluation of pitch and linewidth. The thickness (i.e., height) factor does play an important role in the contrast of SEM imaging and the shape of the SE profile in these two-material systems. The mechanism of the influence of insulating layer thickness for imaging was studied in detail. In addition, the SiO2/Si pitch structure with a real rough surface was also studied. This work has significant implications for the study of various kinds of two-material systems and could help to optimize the pitch and gate linewidth measurements.

The use of concrete-recycled aggregates to produce high-performance concrete is limited by insufficient correlation between resulting microstructure and its influence on mechanical performance reproducibility. This work addresses this issue in a sequential approach: concrete microstructure was systematically analyzed and characterized by scanning electron microscopy and results were correlated with concrete compressive strength and water absorption ability. The influence of replacing natural aggregates (NA) with recycled concrete aggregates (RCA), with different source concrete strength levels, of silica fume (SF) addition and of mixing procedure was tested. The results show that the developed microstructure depends on the concrete composition and is conditioned by the distinct nature of NA, recycled aggregates from high-strength source concrete, and recycled aggregates from low-strength source concrete. SF was only effective at concrete densification when a two-stage mixing approach was used. The highest achieved strength in concrete with 100% incorporation of RCA was 97.3 MPa, comparable to that of conventional high-strength concrete with NA. This shows that incorporation of significant amounts of RCA replacing NA in concrete is not only a realistic approach to current environmental goals, but also a viable route for the production of high-performance concrete.

Current approaches to reconstruction in atom probe tomography produce results that exhibit substantial distortions throughout the analysis depth. This is largely because of the need to apply a multitude of assumptions when estimating the evolution of the tip shape, and other pseudo-empirical reconstruction factors, which vary both across the face of the tip and throughout the analysis depth. We introduce a new crystallography-mediated reconstruction to improve the spatial accuracy and dramatically reduce these in-depth variations. To achieve this, we developed a barycentric transform to directly relate atomic positions in detector space to real space. This is mediated by novel crystallographic analysis techniques, including: (1) calculating the orientation of a crystal directly from the field evaporation map, (2) tracking pole locations throughout the evaporation sequence, and (3) accounting for the evolving tip radius in a manner that removes the dependence on the geometric field factor. By improving the in-depth spatial accuracy of the atom probe reconstruction, a greater accuracy of the atomic neighborhood relationships is available. This is critical in modern materials science and engineering, where an understanding of the solid solution architecture, precipitate dispersions, and descriptions of the interfaces between phases or grains are key inputs to microstructure–property relationships.

A systematic characterization of a less known Al, Fe, Mn, and Si phase in a SiC particulate-reinforced 2014Al composite (SiCp/2014Al) was performed. In addition to the expected CuAl2 phase, the Al, Fe, Mn, and Si phase was formed as either an adhesion (>1 µm) onto SiC in the as-cast composite, or as a precipitate (<100 nm) in the matrix after hot extrusion. The structure of the phase was identified as cubic by both X-ray diffraction and selected area electron diffraction (SAED). The SAED pattern also indicated that the structure belongs to the Pm$\bar{3}$ space group instead of Im$\bar{3}$. The thermodynamic phase diagram was calculated, confirming the presence of an α-AlFeMn or α-AlFeSi phase in the Al–Fe–Mn and Al–Fe–Si ternary systems, respectively, within the Fe, Mn, and Si content range corresponding to 2014Al. Wavelength-dispersive spectroscopy analysis indicated that the composition of the phase is close to Al12(Fe, Mn)3Si2, in which the Mn/Fe ratio is in the range of 0.6–1.4. The determined Mn/Fe ratio corresponds to the nominal composition of Mn and Fe in the alloy.

Grain boundaries (GBs) play an important role in material behavior, so considerable effort has gone into determining their structure and properties. Studies of GBs have revealed a correlation between the GB energy and expansion of the planes normal to the GB, or the so-called normal volume expansion. In this investigation, the volume expansion at several GBs was experimentally determined using extended energy-loss fine structure (EXELFS) analysis in a scanning/transmission electron microscope, allowing changes in the nearest-neighbor (n.n.) distances to be determined with nanometer spatial resolution. EXELFS performed on three-model GBs showed that the average n.n. distances at the GBs increased with increasing GB energy. Additionally, the total volume expansion at the GBs, calculated using complementary plasmon energy profiles, showed excellent agreement with volume expansions measured using other experimental techniques. Hence, this study demonstrates that EXELFS is a useful technique to measure the normal volume expansion at GBs. When combined with the results from complementary studies on the same GBs using valence electron energy-loss spectroscopy, this work further shows that the GB energy increases in relation to both the decrease in electron density at the GB and an accompanying increase in specific volume expansion at the GB.

Electron microprobe trace element analysis is a significant challenge. Due to the low net intensity of peak measurements, the accuracy and precision of such analyses relies critically on background measurements, and on the accuracy of any pertinent peak interference corrections. A linear regression between two points selected at appropriate background positions is a classical approach for electron probe microanalysis (EPMA). However, this approach neglects the accurate assessment of background curvature (exponential or polynomial), and the presence of background interferences, a hole in the background, or an absorption edge can dramatically affect the results if underestimated or ignored. The acquisition of a quantitative wavelength-dispersive spectrometry (WDS) scan over the spectral region of interest remains a reasonable option to determine the background intensity and curvature from a fitted regression of background portions of the scan, but this technique can be time consuming and retains an element of subjectivity, as the analyst has to select areas in the scan which appear to represent background. This paper presents a new multi-point background (MPB) method whereby the background intensity is determined from up to 24 background measurements from wavelength positions on either side of analytical lines. This method improves the accuracy and precision of trace element analysis in a complex matrix through careful regression of the background shape, and can be used to characterize the background over a large spectral region covering several elements to be analyzed. The overall efficiency improves as systematic WDS scanning is not required to assess background interferences. The method is less subjective compared to methods that rely on WDS scanning, including selection of two interpolation points based on WDS scans, because “true” backgrounds are selected through an exclusion method of possible erroneous backgrounds. The first validation of the MPB method involves blank testing to ensure the method can accurately measure the absence of an element. The second validation involves the analysis of U-Th-Pb in several monazite reference materials of known isotopic age. The impetus for the MPB method came from efforts to refine EPMA monazite U-Th-Pb dating, where it was recognized that background errors resulting from interference or strong background curvature could result in errors of several tens of millions of years on the calculated date. Results obtained on monazite reference materials using two different microprobes, a Cameca SX-100 Ultrachron and a JEOL JXA-8230, yield excellent agreement with ages obtained by isotopic methods (Thermal Ionization Mass Spectrometry [TIMS], Sensitive High-Resolution Ion MicroProbe [SHRIMP], or Secondary Ion Mass Spectrometry [SIMS]). Finally, the MPB method can be used to model the background over a large spectrometer range to improve the accuracy of background measurement of minor and trace elements acquired on a same spectrometer, a method called the shared background measurement. This latter significantly improves the accuracy of minor and trace element analysis in complex matrices, as demonstrated by the analysis of Rare Earth Elements (REE) in REE-silicates and phosphates and of trace elements in scheelite.

Mineral particles in bone are interlaced with collagen fibrils, hindering the investigation of bioapatite crystallites (BAp). This study utilized a special whale rostrum (the most highly mineralized bone ever recorded) to measure the crystallites of bone BAp via long-term dissolution in water. The BAp in the rostrum has a low solubility (6.7 ppm Ca and 3.8 ppm P after 150 days dissolution) as well as in normal bones, which leads to its Ksp value of ~10−53. Atomic force microscopy results show tightly compacted mineral crystallites and confirm the low amount of collagen in the rostrum. Additionally, the mineral crystallites demonstrate irregular plate-like shapes with variable sizes. The small crystallites (~11 × 24 nm) are easily detached from BAp prisms, compared with the large crystallites (~50 nm). Moreover, various orientations of crystallites are observed on the edge of the prisms, which suggest a random direction of mineral growth. Furthermore, these plate-like crystallites prefer to be stacked layer by layer under weak regulation from collagen. The morphology of rostrum after dissolution provides new insights into the actual morphology of BAp crystallites.

The choice of materials that constitute electrodes and the way they are interconnected, i.e., the microstructure, influences the performance of lithium-ion batteries. For batteries with high energy and power densities, the microstructure of the electrodes must be controlled during their manufacturing process. Moreover, understanding the microstructure helps in designing a high-performance, yet low-cost battery. In this study, we propose a systematic algorithm workflow for the images of the microstructure of anodes obtained from a focused ion beam scanning electron microscope (FIB-SEM). Here, we discuss the typical issues that arise in the raw FIB-SEM images and the corresponding preprocessing methods that resolve them. Next, we propose a Fourier transform-based filter that effectively reduces curtain artifacts. Also, we propose a simple, yet an effective, global-thresholding method to identify active materials and pores in the microstructure. Finally, we reconstruct the three-dimensional structures by concatenating the segmented images. The whole algorithm workflow used in this study is not fully automated and requires user interactions such as choosing the values of parameters and removing shine-through artifacts manually. However, it should be emphasized that the proposed global-thresholding method is deterministic and stable, which results in high segmentation performance for all sectioning images.

A technique to characterize the native passivation layer (NPL) on pure lithium metal foils in a scanning electron microscope (SEM) is described in this paper. Lithium is a very reactive metal, and consequently, observing and quantifying its properties in a SEM is often compromised by rapid oxidation. In this work, a pure lithium energy-dispersive x-ray spectrum is obtained for the first time in a high vacuum SEM using a cold stage/cold trap with liquid nitrogen reservoir outside the SEM chamber. A nanomanipulator (OmniProbe 400) inside the microscope combined with x-ray microanalysis and windowless energy dispersive spectrometer is used to fully characterize the NPL of lithium metal and some of its alloys by a mechanical removal procedure. The results show that the native films of pure lithium and its alloys are composed of a thin (25 nm) outer layer that is carbon-rich and an inner layer containing a significant amount of oxygen. Differences in thickness between laminated and extruded samples are observed and vary depending on the alloy composition.

Understanding and resolving discrepancies between atom probe tomography (APT) and secondary ion mass spectrometry (SIMS) measurements of B dopants in Si-based materials has long been a problem for those in the semiconductor community who wish to measure B within the source/drain SiGe of a device. APT data collection of Si-based materials is typically optimized for Si, which is logical, but perhaps not ideal for field evaporation of B. Increasing the evaporation field well beyond the typically used 28Si2+:28Si+ ratio of approximately 10:1 up to a ratio of ~200:1 is demonstrated to improve B detection while retaining well-matched Si and Ge concentrations with respect to those measured by SIMS. A range of evaporation conditions are examined from a very low field with high laser energy to an extremely high field with extremely low laser energy demonstrating problems at both far ends of the spectrum and a sweet spot when the operating conditions used produce a 28Si2+:28Si+ ratio of approximately 200:1 (in terms of total counts of each ionization state), which is more than an order of magnitude higher than normally used conditions and results in nicely matched B, Si, and Ge APT measurements with those of SIMS.

Although atom probe tomography (APT) reconstructions do not directly influence the local elemental analysis, any structural inferences from APT volumes demand a reliable reconstruction of the point cloud. Accurate estimation of the reconstruction parameters is crucial to obtain reliable spatial scaling. In the current work, a new automated approach of calibrating atom probe reconstructions is developed using only one correlative projection electron microscopy (EM) image. We employed an algorithm that implements a 2D cross-correlation of microstructural features observed in both the APT reconstructions and the corresponding EM image. We apply this protocol to calibrate reconstructions in a Cu(In,Ga)Se2-based semiconductor and in a Co-based superalloy. This work enables us to couple chemical precision to structural information with relative ease.

The trace elements in quartz, Al and Ti, contain considerable information about mineral genesis, and determining their concentrations is of great importance in geology. Electron probe microanalysis has the advantages of non-destructive testing and high spatial resolution; however, it is a challenge to improve the accuracy and precision of trace element detection using this method. The important factors affecting accuracy include the fragility of quartz lattices at high beam currents and the methods used to determine the background. In this paper, the peaks of Al-Kα and Ti-Kα, and their backgrounds, were found to exhibit intensity variations at high beam currents and small beam diameters; therefore, it is necessary to select a large beam diameter (up to 20 µm) to avoid variations in intensity at high currents (500 nA). For background determination of Al, a multipoint background method is proposed to determine the background value, which greatly improves the accuracy of the results. For Ti, the choice of background measurement does not affect the result. In addition, it is verified that the background obtained from other quartz samples can be used as the background of an unknown quartz sample, which reduces the analysis time and minimizes sample damage.

Our group has reported the imprint formation of biological material on polycarbonate nuclear track detectors by UV-C exposure, which is used as an approach to simultaneously visualize cell imprints and nuclear tracks coming from the boron neutron capture reaction. Considering that the cell nucleus has a higher UV-C absorption than the cytoplasm and that hematoxylin preferentially stains the nucleus, we proposed to enhance the contrast between these two main cell structures by hematoxylin staining before UV-C sensitization. In this study, several experiments were performed in order to optimize UV-C exposure parameters and chemical etching conditions for cell imprint formation using the SK-BR-3 breast cancer cell line. The proposed method improves significantly the resolution of the cell imprints. It allows clear differentiation of the nucleus from the rest of the cell, together with nuclear tracks pits. Moreover, it reduces considerably the UV-C exposure time, an important experimental issue. The proposed methodology can be applied to study the boron distribution independently from the chosen cell line and/or boron compounds.